The present invention relates to a tapered roller bearing apparatus and a hub unit.
A vehicle wheel is rotatably supported by a rolling bearing with respect to a suspension device. Heavy vehicles such as truck and bus are generally supported by double row tapered roller bearing with respect to the suspension device.
As to the bearing apparatus, there has been proposed a tapered roller bearing apparatus called a third generation hub unit that is designed to reduce a cost by reducing the number of components.
As shown in FIG. 6, the tapered roller bearing apparatus includes first and second outer-ring raceways 2 and 3 which are provided in an inner circumferential surface of an outer ring 1; first and second inner-ring raceways 5 and 6 which are provided in an outer circumference of a hub main body 4 as an inner ring so as to be opposed to the outer-ring raceways 2 and 3; and a plurality of tapered rollers 7 which are arranged between the outer-ring raceways 2 and 3 and the inner-ring raceways 5 and 6 so as to be retained by a cage 8 at the same interval in the circumferential direction.
An attachment portion 9 is provided in the outer circumference of the outer ring 1 so as to fix the outer ring 1 to a suspension device (not shown).
Meanwhile, the hub main body 4 includes an inner shaft 4a and an inner ring member 13. At this time, a flange portion 10 to which a vehicle wheel-side member such as a rotor of a brake or a wheel is attached by a bolt (not shown) is provided in one end of the inner shaft 4a so as to outwardly extend in the diameter direction. On the other hand, a small-diameter cylindrical portion 12, to which the inner-ring member 13 having the second inner-ring raceway 6 formed in the outer circumference thereof is fitted, is provided in the other end of the inner shaft 4a. The first inner-ring raceway 5 is formed between the small-diameter cylindrical portion 12 and the flange portion 10 in the outer circumferential surface of the inner shaft 4a. 
A large rib portion 11 having a guide surface 11a which comes into sliding contact with a large-diameter end surface 7a of the tapered roller 7 is formed in an end of the first inner-ring raceway 5 close to the flange portion 10. At this time, a clearance between the outer ring 1 and the inner shaft 4a is sealed by a seal member 14.
Incidentally, in the tapered roller bearing apparatus, in order to mainly ensure performance of the first inner-ring raceway 5, a high-frequency hardening is locally performed on a portion including the lower part of the flange portion 10, the large rib portion 11, the first inner-ring raceway 5, and the small-diameter cylindrical portion 12 to thereby form a surface-hardened layer thereon. Since an outer circumferential corner portion of the large rib portion 11, that is, a portion surrounded by an outer circumferential surface 11b and the guide surface 11a of the large rib portion 11 forms an acute edge, induction current is excessively concentrated on the edge portion during the high-frequency hardening to thereby become an overheat state. As a result, a problem arises in that a crack occurs in a portion around the large rib portion 11, that is, a relief portion 15 formed in the corner portion of the first inner-ring raceway 5 and the guide surface 11a of the large rib portion 11.
For this reason, a technique has been proposed in which the outer circumferential corner portion of the large rib portion 11 is set to an obtuse angle so as to prevent a crack by restricting an overheat state of the large rib portion 11 (see JP-A-2005-3111). According to the bearing apparatus disclosed in JP-A-2005-3111, since the outer circumferential corner portion of the large rib portion is set to an obtuse angle, volume of the outer circumferential portion of the large rib portion including the outer circumferential corner portion of the large rib portion becomes large to thereby increase a heat capacity. Accordingly, local overheat does not occur, thereby restricting or preventing a crack from occurring.
However, in the tapered roller bearing apparatus disclosed in JP-A-2005-3111, since the outer circumferential surface of the hub main body is simply formed into the inclined surface from the position around the lower part of the flange portion to the guide surface of the large rib portion in order to allow the outer circumferential corner portion of the large rib portion to be set to an obtuse angle, a problem may arise in that sealing performance of the seal member, which is disposed in the inclined surface while contacting therewith, deteriorates.